A more recent approach in dentistry is to treat patients by performing multiple required dental procedures during a single dental office visit. For example, in an approach commonly referred to as “quadrant dentistry,” multiple (preferably all) dental conditions existing in a particular dental quadrant are treated together in a single, continuous procedure. This optimizes chair time for the dentist and minimizes patient visits. Combining multiple procedures together into a single visit (e.g., based on dental quadrant(s)) requires injection of multiple cartridges of anesthetic. Current self-aspirating syringes inject one cartridge of anesthetic per injection, using a plunger or harpoon style system that delivers the anesthetic to the area to be anesthetized. Thus, the current practice for dispensing several cartridges of anesthetic is to load a first cartridge into the syringe, inject the first cartridge, withdraw the syringe, remove the spent cartridges from the syringe, reload the syringe with a second cartridge, and inject the second cartridge. This procedure is repeated for all additional cartridges that are required to be injected for the particular operations being performed.
The above-described practice has several shortcomings. For example, the risk to of needle sticks to dental team members increases with the number of times the syringe must be removed and reloaded. Additionally, the fine gage needle used to inject the fluid into the tissue is more likely to become damaged during such reloading procedures. Furthermore, these reloading procedures (which require breakdown of the syringe) increase the amount of time required by such dental procedures. This additional time required to switch out cartridges can be distracting to the dentist, and can be expensive (e.g., in terms of opportunity costs). Furthermore, patients often feel greater discomfort during such reloading procedures, as the repeated lowering of a needle can be an intrusive and intimidating sight to bear.
U.S. Pat. No. 5,542,934 to Silver attempts to address some of the aforementioned problems by providing a syringe that is capable of simultaneously injecting two different cartridges to a patient. In particular, the syringe described in Silver includes two barrels laid side-by-side for receiving two cartridges. By manipulating a single finger ring, a plunger is depressed simultaneously against the two cartridges contained in the two barrels. Thus, the provision of two cartridges does somewhat increase the volume of fluid available for injection, but not to an amount sufficient for many present day procedures that can require three or more cartridges. In addition, the structure of the device of Silver includes a mixing chamber where the fluid exiting each cartridge must pool before traveling to the needle and exiting the device. Such mixing chambers can create difficulties in maintaining a sterile environment within the device.